The proposed project involves: the development of a new synthetic approach (through vinyl allene intermediates) to 1-oxygenated vitamin D analogs and the application of this new method to the synthesis of 3-alkyl-3-deoxy-1 alpha-hydroxyvitamin D3 and various other A-ring analogs (a-homo, A-nor, 3-thia ad 3-oxa analogs); studies on 10,19-dihydrovitamins; structure and function studies of vitamin D agonists and antagonists. The general goals of the project include the development of an understanding of the mechanism of action of vitamin D and the synthesis of potentially useful analogs with high vitamin D or anti-vitamin D activity.